The first five weeks of the college football season have been exhilarating, with craziness almost every Saturday. At first glance, Week 6 appears to offer a respite. There are just two matchups between ranked teams, following a Week 5 slate that had five such games along with several more that pitted high-profile squads.

It’s important to remember, though, that it’s often the weeks that appear weakest on paper that end up producing the most chaos, whether it be upsets nobody saw coming or contenders being pushed to the brink. Considering how the season has gone so far, it wouldn’t surprise at all if this week brings some unexpected results. Either way, it’s fitting that Saturday’s two biggest games involve four teams that have outperformed expectations, because 2015 is unfolding as one of the most topsy-turvy seasons in recent memory.

Here are the five biggest storylines to watch in Week 6:

1. Michigan-Northwestern an unexpected key Big Ten battle

Hardly anyone expected this to be one of the more significant games in the Big Ten this season, but the Wolverines and Wildcats have emerged as legitimate contenders in the conference's East and West division, respectively. Both teams' surprising starts have been fueled by elite defensive play. Northwestern and Michigan rank first and second in the country in scoring defense (7.0 and 7.6 points allowed per game, respectively) and fifth and second in total defense (247.4 and 184 yards allowed per game, respectively). Northwestern’s rise has been especially dramatic—the program has finished in the top 50 in total defense just once in the past five seasons.

Linebacker Anthony Walker has emerged as a star for Pat Fitzgerald’s team, while Michigan has been led by its deep, disruptive D-line. Considering the strength of the defenses and the relative weakness of the offenses in this game, it might not be a stretch to say that the first to score a touchdown will win. Even if there are more points than that, the game could come down to whichever D can produce more momentum-shifting plays and/or turnovers. The winner will remain in strong position in its division, but the loser still has plenty of time to regroup and build on its better-than-expected start.

Speaking of defense, Cal has struggled to field a quality one in recent years. The Bears have placed 124th, 124th and 95th in total defense the last three seasons, helping result in the program’s fewest wins in a three-year stretch since 1999-01. This season Cal is 5–0, already matching last season’s win total, and while star quarterback Jared Goff and Sonny Dykes’s potent Air Raid offense rightfully get most of the headlines, the defense will likely be the key in maintaining the team’s hot start.

The Bears are improved so far, currently rating 72nd in the country in total D and 78th in yards allowed per play, but they haven’t done enough to convince anyone they have staying power. (Case in point: Texas scored a season-high 44 points in its loss to Cal in Week 3.) Utah offers Cal a chance to prove that it’s stout enough to compete all year in the Pac-12. With Devontae Booker, Travis Wilson and Co. coming off a 62-point explosion at Oregon, slowing them down will be no easy task. But Cal just has to do enough to give Goff and the offense a chance. Accomplish that, and the Bears might pull off an upset that shakes up the conference race.

3. Miami has an opportunity for much-needed signature victory

Miami may be 3–1, but the natives remain restless in South Florida, especially regarding head coach Al Golden. The “Fire Al Golden” airplane banner seen at three of the Hurricanes’ games this year, including their road tilt at Cincinnati, is proof of that. The loss to the underdog Bearcats was the latest disappointment in Golden’s four-plus seasons, leaving him and his program in need of a big win to generate some positive momentum.

That’s why Saturday presents such a big opportunity for Miami, especially given the recent optics of the rivalry. The Canes blew a 16–0 lead to Florida State last year and have lost five in a row to the Seminoles overall, their worst streak since losing seven straight from 1963-72. Beyond that, Golden has gone 0­­–12 with Miami against teams that finished the season ranked. Miami’s the definitive underdog on Saturday, but this edition of FSU appears much more beatable than the past two Seminoles teams. Plus, Florida State running back Dalvin Cook, the centerpiece of the team’s offense, could be out with a hamstring injury, which would be a big boon for the Hurricanes’ chances. Pull the upset, and Miami will both quell the heat on Golden (at least temporarily) and re-establish momentum after last week’s setback.

4. Oklahoma looks to avoid a major letdown in the Red River Shootout

Oklahoma is coming off a convincing win over a West Virginia team that looked like it could be a surprise challenger in the Big 12. The Sooners’ revamped offense was especially impressive, putting up 427 total yards and 37 points on one of the top-rated defenses in the country. Meanwhile, Texas is as down as it’s been in recent memory, with its poor on-field results being combined with off-field controversies involving halftime tweeting, talk of an upperclassmen/freshman rift and even a legal battle with Oklahoma State.

This is precisely why the Sooners have to be so careful against the Longhorns. Rivalry games are always tricky—Oklahoma can attest, as it struggled to put away inferior Texas teams the last two seasons—and UT will be desperate for a season-saving win. It’s perhaps just as likely that Texas folds as it is the Longhorns circle the wagons and come up with an inspired performance, but still, the possibility of the latter exists. Oklahoma will be the clear favorite each of the next five weeks, and it can’t afford to look ahead to its three-game finishing kick of Baylor, TCU and Oklahoma State. Since crazy things tend to happen in rivalries, this week could be the biggest test of the Sooners’ focus until then.

5. TCU attempts to keep compiling style points for its playoff résumé

TCU’s final two games of the season (at Oklahoma and home against Baylor) are its most important for determining its College Football Playoff chances, but in a season that could end up with a muddled playoff picture, it’s important the Horned Frogs look good in winning the games they’re supposed to. Narrow wins like TCU’s against Texas Tech can be used as ammunition when résumés are ultimately compared. Gary Patterson’s team is now entering its third of four games against subpar competition before its bye, and after looking dominant against a sinking Texas team last week, it has a chance to keep that going at Kansas State.

Winning in Manhattan won’t be a given as long as Bill Snyder is around, and this year is no exception. In an alternate universe where referees don’t falsely award first downs, the Wildcats beat Oklahoma State last week and enter Saturday night’s showdown 4–0 and possibly nationally ranked. Still, this is a good opportunity for a relatively easy, persuasive win. KSU is third in the country in rushing defense but a woeful 116th in passing defense and has been hit hard by injuries at quarterback, having already used five players at the position. Winning this game handily will help firm up TCU’s status as a chief playoff contender before its bigger games in November.